1. Field of the Invention
The present invention relates to a hollow sealing structure for a functional element, such as a microelectric machine part, micromachine packaging, etc., and a manufacturing method for the hollow sealing structure.
2. Description of the Related Art
There are known hollow sealing structures, such as an electric machine part for sealing an operational functional element mounted on a substrate in a hollow space. For example, a hollow sealing structure 21 shown in FIG. 18 is composed of a base substrate 22, a dielectric layer 23, a functional element 24, a signal conducting member 25, a gap portion 26, and first and second sealing members 27 and 28 as sealing members.
The functional element 24 has, for example, a doubly-supported beam structure such that the central part of a beam is separated from the signal conducting member 25 by several micrometers. The signal conducting member 25 of Au or the like is formed on the dielectric layer 23 immediately under the functional element 24. The functional element 24 is formed of TiN or Al with high elasticity. If it is subjected to a driving force, such as an electrostatic force, the functional element 24 is deformed so as to approach the signal conducting member 25. If the driving force is removed, the functional element 24 is restored to its original position by its own elasticity. Thus, the functional element 24 fulfills functions, such as variable capacitance change, switching, etc., as the distance from the signal conducting member 25 changes depending on the driving force.
A technique for sealing the functional element 24 in a hollow space for the ease of operation and protection is described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-207959. According to this technique, a thin film prepared by a film forming process is used to reduce the manufacturing cost and size of the element. As shown in FIG. 13, a sacrificial layer (first layer) 32 is formed on a substrate that is composed of the base substrate 22 and the dielectric layer 23. Then, the functional element 24 is formed on the sacrificial layer 32, as shown in FIG. 14. As shown in FIG. 15, a sacrificial layer (second layer) 33 is formed on the functional element 24 that is formed on the sacrificial layer 32. As shown in FIG. 16, opening portions 27a for the introduction of an etching material for sacrificial layer removal are formed in the first sealing member 27.
If the second sealing member 28 (mentioned later) is prepared by a film forming method, such as sputtering, vapor deposition, or CVD, a film material is deposited immediately under the opening portions 27a. Therefore, the opening portions 27a must be spaced from the functional element. Further, spaces for the circulation of the etching material must be secured between the upper surface of the dielectric layer 23 and those parts of the lower surface of the first sealing member 27 which are situated near the opening portions 27a. Then, the sacrificial layers 32 and 33 are thoroughly removed by introducing the etching material for sacrificial layer removal through the opening portions 27a, as shown in FIG. 17. Finally, the opening portions 27a are closed by forming the second sealing member 28 on the first sealing member 27, as shown in FIG. 18. Thereupon, a hollow sealing structure is completed such that the functional element is sealed in the hollow space, as shown in FIG. 18.
However, the above-described technique involves the following problems. In the aforesaid structure, the first sealing member must be made large enough to secure the circulation of the etching material for sacrificial layer removal. Accordingly, the hollow sealing structure and the sacrificial layers therein are increased in size, and the removal of the sacrificial layers takes longer. Further, a load produced by a pressure difference between the inside and outside also increases, thereby possibly causing contact with and breakage of the functional element.
The present invention has been made in order to solve these problems, and its object is to provide a hollow sealing structure and a manufacturing method therefor, capable of miniaturization of the hollow sealing structure and reduction in time for the removal of sacrificial layers therein.